40 Eridani

40 Eridani. The primary (A) is the bright star to
the right. Component C is just visible above and to the right of component
B in this image

A nearby trinary (three-star) system in the constellation Eridanus.
It is also known as Omicron2 Eridani or Keid.

40 Eridani A is an orange main-sequence K star
some 4 billion years old. 40 Eridani B is a white
dwarf, the first such star to be discovered. 40 Eridani C is a red
dwarf and also a flare star with the
variable star designation DY Eridani. Components B and C orbit around each
other and, as a pair orbit the primary, which lies about 400 astronomical
units away.

40 Eridani A is the star around which the Vulcan
homeworld orbits in the fictional universe of Star
Trek. Astronomers have recently considered if this star might actually
have any Earthlike planets and, if so, they might be capable of supporting
life.

The search for Vulcan

The first problem to consider is whether an Earth-mass planet could have
formed around 40 Eridani A, which has two stellar companions tugging at
it. The answer to this seems to be "yes". On the Jet Propulsion Laboratory's
"PlanetQuest" website, planetary theorist Sean Raymond of the University
of Colorado, Boulder, commented: "Since the three members of the triple
star system are so far away from each other [hundreds of astronomical units],
I see no reason why an Earth-mass planet would not be able to form around
the primary star, 40 Eridani A."

Comparison of the habitable zone of 40 Eridani A
with that in our solar system. Image credit: NASA

If such a planet exists, then in order for it to be able to support life
as we know it, or advanced Vulcans like Mr. Spock, it would need to have
an orbit that would allow it to have liquid water
on its surface. This means it would have to move within the region around
known as the habitable zone. Because the
primary star is a K dwarf that is cooler and dimmer than the Sun, the "sweet
spot" for Vulcan would be about 0.6 astronomical units from the star –
slightly less than the distance of Venus from the Sun. The fact that 40
Eridani A emits a more reddish (longer wavelength) light than the Sun might
have consequences for its inhabitants, especially for any plant life present.

It has been calculated that, when launched, NASA's SIM PlanetQuest satellite
would be able to definitively determine whether there is an Earth-mass planet
orbiting in the habitable zone around 40 Eridani A, and could also determine
its orbit. If a positive identification were made, it could be followed
up by NASA's Terrestrial Planet Finder mission, which would not only be
able to take a rudimentary picture of the planet, but also could search
for signatures of life such as methane and ozone.